Bovine Mastitis

BY W. T. MILLER ^

BOVINE MASTITIS is responsible for enormous losses, through reduced milk production and in other ways, in our dairy herds. Here is a sound program of control based on early detection of the disease, segrega- tion of diseased cows, and use of sanitary measures.

BOVINE MASTITIS is an extremely serious disease of dairy cattle. The annual economic loss to dairymen from loss of cows, decreased milk production, and poor-quality milk is tremendous. In addition, cer- tain human diseases can be contracted through the use of unpasteur- ized milk from affected cows. To reduce these losses and to improve both the quantity and quality of milk are of the greatest importance at this time. Mastitis means inflammation of the udder from any cause. There are two forms of the disease, acute and chronic. The latter is the more common, but it is not readily recognized. The acute form, commonly known as garget, is familiar to every dairyman. The affected quarter is reddened, swollen, hot, and painful. The secre- tion is very much reduced and varies from a watery, blood-tinged fluid containing a few solid particles to thick, yellow, ropy material. In the past an attack of acute mastitis was thought to be tempo- rary, and it was believed that when it passed, recovery was complete. Actually, in most cases the acute symptoms represent a flare-up of the chronic form already present in the quarter. Recovery from an acute attack usually means a return to the chronic state. When the average dairy herd is examined for mastitis, it is not unusual to find the chronic form of the disease in one or more quarters of the udders of half the cows. Because of the lack of easily recognized symptoms the owner may be unaware of the extent of the disease. On inquiry, however, the infected cows will be found to have had acute attacks, as a rule at the beginning or end of a lactation period. They are usually short milkers.

iW. T. Miller is Veterinarian, Animal Disease Station, Bureau of Animal Industry. 518 Bovine Mastitis 519

Mastitis is an infectious disease. Certain kinds of bacteria enter the openinteat, where they cause a mild or low-triade inflammation. In the course of time the bacteria spread to other parts of the ghmd, and the inflammation extends until finally the entire quarter is affected. Acute attacks usually occur as the infection progresses. As a result of the inflammation, the composition of the milk is chaiiged. Although the milk may appear normal, the percentages of butterfat, lactose (milk sugar), casein, and possibly other elements are decreased. On the other hand the number of leucocytes, the salt content, the number of bacteria, and the products resulting from inflammation and bacterial activity increase. A change in the char- acter of the udder tissue itself also occurs. The normal secretory tissue is gradually replaced by nonsecretory, scar (fibrous) tissue. Finally the quarter loses its soft, pliable quality, and hard areas, circuniscribed or diffuse, appear in the vicinity of the milk cistern. In advanced cases the quarter becomes hardened throughout, and there is an almost complete loss of secretory tissue. With the change in the character of the udder tissue, milk produc- tion drops, which accounts for shortened lactation periods. The time required for this change to occur varies considerably, depending on the virulence of tlie invading bacteria, the natural resistance of the animal, the number of acute attacks, and management and feeding practices. In some cases of chronic mastitis the animal may pass through a number of lactation periods before the disease manifests itself. On the other hand, many cows become entirely useless in a comparatively short time,

BACTERIA CAUSING MASTITIS

Bovine mastitis can be caused by a number of different kinds of bacteria. Of greatest importance are the streptococci, including several species that are responsible for such diseases in man as scarlet fever and septic sore throat. Fortunately, infection with these spe- cies occurs infrequently and usually as a result of the bacteria having been carried to the end of the teat on the hands of an infected milker. Bacteria of these species do not tend to spread through the herd. On the other hand the streptococci most connnonly found in mastitis rarely cause disease in man. However, they spread readily from cow t-o cow on the milkers' hands or the cups of the milking machine. Once established these streptococci usually remain in the quarter for the rest of the life of the animal. Aninfected cow is therefore a constant source of danger for the other cows in the herd. Next in importance as a cause of mastitis are the staphjdococci. Several species are known, and they undoubtedly cause many more cases of mastitis than is generally realized. Staphyloccxîci, like strep- tococci, cause the clironic form of the disease, but they are not likely to persist in the udder for as long a time as the streptococci. Acute attacks which may terminate in the death of the animal occur fre- quently in staphylococcal mastitis. 520 Yearbook of Agriculture, 1942 Various other types of bacteria arc found in occasional outbreaks of the disease. For the most part these types cause acute mastitis accompanied by systemic disturbance, and not infrequently the ani- mal dies. In most cases of this kind the infection leaves the udder after recovery. When these outbreaks occur, they constitute a serious problem through loss of function of quarters and death of cows. Fortunately they appear only sporadically.

DIAGNOSIS Early detection of diseased cows is extremely important. Acute attacks of mastitis can be diagnosed readily by clinical symptoms, but the chronic form presents some difficulty. Tests that largely solve this problem are now available. Diagnosis of mastitis in individual cows and recommendations for controlling the spread of the disease are functions of the veterinarian. Responsibility for carrying out sanitary measures, early detection of subsequent cases of mastitis, and proper disposition of diseased animals rests with the owner or herdsman. It is essential, therefore, that he should have some knowl- edge of the more common tests and understand their significance. Tests for easy routine use must be easily applied and reasonably accurate. Two such tests are now in use in many herds. One is the strip-cup test. In this test several streams of milk are drawn from a quai-ter onto a fine-mesh wire screen immediately before the animal is milked. The appearance of clots or flakes or of watery or off-color milk on the screen is evidence of mastitis. As in other tests of simi- lar nature, the accuracy of results obtained with the strip-cup test improves with frequent usage. To obtain best results the cup should be used jDefore each milking, or once a day at the very least. With this test mastitis can frequently be detected in previously healthy cows, and bad milk can be kept out of the general supply. The second test is the brom thymol-blue, or thybromol, test. Changes in the milk are detected by variations in color when the dye solution from which the test derives its name is mixed with it. Milk drawn from a healthy quarter is slightly acid. When a few drops of the dye are added to it, a pale yellowish-green color results. Milk from a diseased quarter is alkaline, and this is indicated by a green color when the dye is added. Different shades of green may be en- countered, depending on the degree of alkalinity. The more alkaline the milk, the darker the shade of green becomes. An intense yellow may be observed occasionally. This indicates a very acid condition and is usually accompanied by gross alteration in the appearance of the secretion. Frequent use of the brom-thymol-blue test also in- creases its effectiveness materially.

PREVENTION Since curative measures are not entirely effective, a program for controlling the spread of mastitis bacteria from diseased to healthy cows affords an effective and practical means of dealing with the disease. In most cases the bacteria are carried on the milkers' hands or in the teat cups of the milking machine. When a healthy animal Bovine Mastitis 521 is milked immediately after an infected one, the mastitis bacteria are left on tlie teats of the healthy cow, in which repeated exposure will eventually produce the disease. The purpose of the control program, therefore, is to avoid exposure of healthy cows during milking. Detection of all cows with mas- titis is the first step. Cows with extensive induration (hardening) of the udder should be removed immediately from the herd. They are unprofitable for milk production, are subject to recurrent acute attacks, and provide a constant source of infection for other cows in the herd. The remaining diseased and healthy animals should then be separated into two groups. Complete segregation of the groups in separate barns with sei)arate milkers is the most desirable arrange- ment. This is not absolutely necessary, however, if strict attention is given to the order of milking and other essential details of the program. The group of cows with healthy udders must always be milked before the infected group. When first-calf heifers are added to the herd, they should be placed with the clean cows unless they show* signs of mastitis. Few heifers come into lactation infected with mastitis bacteria. Cows placed in the two groups should be main- tained in them through subsequent lactation periods unless evidence of mastitis is found in members of the healthy group. Should the routine tests indicate the presence of mastitis in a healthy cow, it must be placed in the diseased croup without delay. Once in the infected group, the animal nuist be kept there as long as it stays in the herd. Infected cows should be sold as soon as they become un- profitable or if they suffer recurrent acute attacks. Certain sanitary measures nuist be included in the program along with strict observance of the milking order. Individual cloths dipped in fresh hypochlorite solution (200 to 400 parts of chlorine per million) should be used to wipe the udder, teats, and flanks of each cow before milking. These cloths must never be replaced in this solution after use. Between milkings they should be washed, steril- ized by boiling or steaming, and dried. After the cow is milked, each teat must be di])ped in a small quantity of fresh hypochlorite solu- tion of the strength indicated. This removes the drop of milk from the end of tlie teat and also repels flies. The solution should be discarded after being used for one cow. Proper feeding nuist also be considered. Feeding a high-protein grain ration nuist be avoided, particularly for cows with mastitis or exposed to the disease. Such feed apparently overstimulates the udder and predisposes it to infection, while infected cows receiving such a ration are more subject to acute attacks and the secretion of abnormal milk. These recurrent attacks lead to more rapid deteriora- tion of the udder. When cows with mild cases of chronic mastitis are fed and managed properly, they may remain in the herd for some time as profitable producers, but they must always be recognized as a source of danger to healthy cows. Protection of the udder from injury and infection is of equal im- portance. Adequate stall space and ample bedding are absolute ne- cessities to protect the teats and udder from being stepped on and 522 Yearbook of Agriculture, 1942 from being bruised or chilled when the animals lie down. Floors and passageways should be so constructed as to give the cows good footing. To keep down infection, floors and stalls must be waished regularly and disinfected with 3- to 5-percent lye solution. As an additional safeguard, liberal use of lime or superphosphate in back of the stalls and in the gutters is important.